SDN-based channel estimation for multiplexing between LOS mmWaves NLOS sub-6 GHz and FSO

ABSTRACT

A system for providing small cell backhaul communication includes a small cell backhaul network including a plurality of small cell network nodes. At least one mmWave transceiver at each of the plurality of small cell network nodes establishes communication links with other small cell network nodes within the small cell backhaul network. A software defined network (SDN) controller for controls communication link configuration by the at least one mmWave transceiver between the plurality of small cell network backhaul nodes of the small cell backhaul network. The link configurations are established by the SDN controller using mmWave communications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.62/381,071, filed on Aug. 30, 2016, entitled AN SDN-BASED CHANNELESTIMATION FOR MULTIPLEXING BETWEEN LOS MMWAVES, NLOS SUB-6 GHZ AND FSO.This application also claims the benefit of U.S. Provisional ApplicationNo. 62/381,073, filed on Aug. 30, 2016, entitled USING LTE CONTROLCHANNEL TO SEND OPENFLOW MESSAGE DIRECTLY TO SMALL CELLS TO REDUCELATENCY IN AN SDN-BASED MULTI-HOP WIRELESS BACKHAUL NETWORK. U.S.Application Nos. 62/381,071 and 62/381,073 are incorporated by referenceherein in their entirety.

TECHNICAL FIELD

The present invention relates to small cell communications networks, andmore particularly, for establishing communication links in small cellcommunications networks using SDN-based channel estimation.

SUMMARY

The present invention, as disclosed and described herein, in one aspectthereof, comprise a system for providing small cell backhaulcommunication includes a small cell backhaul network including aplurality of small cell network nodes. At least one mmWave transceiverat each of the plurality of small cell network nodes establishescommunication links with other small cell network nodes within the smallcell backhaul network. A software defined network (SDN) controllercontrols communication link configuration by the at least one mmWavetransceiver between the plurality of small cell network backhaul nodesof the small cell backhaul network. The link configurations areestablished by the SDN controller using mmWave communications.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to thefollowing description taken in conjunction with the accompanyingDrawings in which:

FIG. 1 illustrates the manner in which a backhaul network interconnectsan edge network and a core network;

FIG. 2 illustrates a network function virtualization;

FIG. 3 illustrates a network function virtualization architecturalframework;

FIG. 4 illustrates software defined network architecture;

FIG. 5 illustrates a software defined network function virtualizationsystem;

FIG. 6 illustrates a flow diagram describing a process for provisioningfunctions;

FIG. 7 illustrates an example of a service chaining process;

FIG. 8 illustrates a wired backhaul network;

FIG. 9 illustrates a wireless backhaul network;

FIG. 10 illustrates a manner for using an SDN-based system for creatingconnections with the small cell network;

FIG. 11 illustrates a heterogeneous network;

FIG. 12 illustrates communications between an SDN controller and a smallcell using OpenFlow messages;

FIG. 13 illustrates a block diagram of a Backhaul Network KeyPerformance Indicator;

FIG. 14 is a flow diagram illustrating the process for link repair;

FIG. 15 illustrates a small cell backhaul network;

FIG. 16 illustrates a small cell node having a primary link and one ormore backup links;

FIG. 17 illustrates a small cell node including means for multiplexingbetween multiple transceiver types;

FIG. 18 illustrates an SDN-based architecture for link generation;

FIG. 19 illustrates a small cell node implementing fast localrestoration within its data plane layer;

FIG. 20 illustrates a flow diagram describing the process forimplementing SDN-based local repair; and

FIG. 21 illustrates a flow diagram describing the process for detectinglink state and for the transmission on primary and backup links.

DETAILED DESCRIPTION

Referring now to the drawings, wherein like reference numbers are usedherein to designate like elements throughout, the various views andembodiments of using LTE control channel to send openflow messagedirectly to small cells to reduce latency in an SDN-based multi-hopwireless backhaul network are illustrated and described, and otherpossible embodiments are described. The figures are not necessarilydrawn to scale, and in some instances the drawings have been exaggeratedand/or simplified in places for illustrative purposes only. One ofordinary skill in the art will appreciate the many possible applicationsand variations based on the following examples of possible embodiments.

Referring now to FIG. 1, there is illustrated the manner in which abackhaul network 102 is used for interconnecting an edge network 104with a core network 106. In a hierarchical network the backhaul network102 comprises the intermediate links between the core network 106(backbone network) and the small subnetworks at the edge of the entirehierarchical network. The backhaul network 102 carries packets/data toand from the core network 106. For example, in a telecommunicationsnetwork cell phones communicating with a cell tower constitute a localsubnetwork. The connection between the cell tower and the rest of theworld begins with a backhaul links to the core of the Internet serviceprovider network. Backhaul networks 102 may be used to describe theentire wired part of the network, although some networks have wirelessinstead of wired backhaul, in whole or in part, for example usingmicrowave bands, mesh networks and edge network topologies. The backhaulnetwork 102 may use high-capacity wireless channels to get packets tothe microwave or fiber links.

Backhaul networks 102 may use a variety of technologies. The choice ofbackhaul technology must take into account parameters such as capacity,cost, reach and the need for such resources as frequency spectrum,optical fiber, wiring or rights-of-way. Generally, backhaul solutionscan largely be categorized into wired (leased lines or copper/fiber) orwireless (point-to-point, point to multipoint over high-capacity radiolinks). Wired solutions are usually very expensive and often impossibleto deploy in remote areas. This makes wireless a more suitable and/orviable option. Multi-hop wireless architecture can overcome the hurdlesof wired solutions by creating efficient large coverage areas withgrowing demand in emerging markets where cost is often a major factor indeciding technologies. Wireless backhaul solutions are able to offercarrier grade services which are not easily feasible with wired backhaulconnectivity. Backhaul technologies include free space optics,point-to-point microwave radio relay transmission (terrestrial or bysatellite), point to multipoint microwave access technologies, such asLMDS, Wi-Fi, WiMAX, DSL variants such as ADSL and SHDSL, PDH and SDHLasse Esso and ET interfaces, such as (fractional) E1/T1, E3, T3,STM-1/OC-3, etc. and ethernet. The system such as that more fully hereinbelow may also be used within the systems such as that describe in U.S.patent application Ser. No. 14/882,085 entitled APPLICATION OF ORBITALANGULAR MOMENTUM TO FIBER, FSO AND RF filed on Oct. 15, 2015 which isincorporated herein by reference in its entirety to transmitinformation.

In an additional to the plane wave embodiments that are disclosed in thedescribed system for SDN-based channel estimation for multiplexingbetween LOS mmWaves, NLOS sub-6 GHz and FSO described herein, a systemfor implementing the twisted waves generated by the application oforthogonal functions to a plane wave may also be utilized. For example,the various embodiments disclosed in U.S. patent application Ser. No.15/216,474 entitled SYSTEM AND METHOD FOR COMBINING MIMO ANDMODE-DIVISION MULTIPLEXING filed on Jul. 21, 2016 and U.S. patentapplication Ser. No. 15/144,297 entitled SYSTEM AND METHOD FORCOMMUNICATION USING ORBITAL ANGULAR MOMENTUM WITH MULTIPLE LAYER OVERLAYMODULATION filed on May 2 2016, each of which is incorporated herein byreference in their entirety may be used.

Using the system such as that described herein with respect to anSDN-based channel estimation for multiplexing between LOS mmWaves, NLOSsub-6 GHz and FSO, the FSO, RF, sub-6 GHz, LOS, non LOS and other typesof signals are multiplexed between to provide the best signal outputdepending upon present operating conditions.

Hybrid (Heterogeneous) networks consist of networks including deviceswherein in the components providing the transmission of data are all thesame but may each be configured using the included operating software toprovide different types of transmissions including but not limited topoint-to-point (P2P); point-to-multipoint (P2MP);multipoint-to-multipoint (MP2MP); etc.

Architecture relates to the various system layers and their applicationto the system from the application layer to the hardware layer such asthat described in U.S. Provisional Application No. 62/371,279, filed onAug. 5, 2016 and entitled ULTRA-BROADBAND VIRTUALIZED TELECOM ANDINTERNET, which is incorporated herein by reference in its entirety.

Multiband as used herein relates to licensed and unlicensed bands asestablished in FCC regulations. Licensed bands include, but are notlimited to, 24 GHz, 30 GHz, 28 GHz and sub-6 GHz. Unlicensed bandsinclude, but are not limited to, U bands(60 GHz), E bands (71-76 GHz,81-86 GHz) and WiFi.

Topology for systems implementing the described components may configurethe nodes in a tree topology or a ring topology. The tree topologycomprises a number of nodes interconnected in a tree structure beginningwith a single node that expands to multiple second nodes and each of thesecond nodes expanding to further multiple third nodes or the singlenode interconnected to each of the other nodes of a network. Each of theother nodes communicates through the single central node. A ringtopology includes a ring connection of all nodes with each nodeconnected only to two adjacent nodes.

A multilayer backhaul network provides for communications using each ofcopper wire, fiber and RF transmissions. RF may use line of sight andnon-line of sight transmissions. Copper may comprise vector bundled(VDSL2) and other types of transmissions. Fiber may use GPON or othertypes of transmissions.

Total Cost Ownership (TCO) can be achieved by using a combination ofsoftware defined networking (SDN), network topology and healing networksto balance factors such as power consumption, capacity andreliability/quality to achieve an optimal operating point. A bestoperating point can be determined that use each of these three factors.

Software Defined Networks and Network Function Virtualization

Diverse proprietary network hardware boxes increase both the capital andoperational expense of service providers while causing problems ofnetwork management. Network function virtualization (NFV) addressesthese issues by implementing network functions as pure software oncommodity and generic hardware. Thus, as shown in FIG. 2, a genericoff-the-shelf hardware 202 may be used to generate a variety of systemapplications 204 that are programmed into the hardware. NFV allowsflexible provisioning, deployment, and centralized management of virtualnetwork functions. Integrated with Software Defined Networks (SDN), thesoftware-defined NFV architecture further offers agile traffic steeringand joint optimization of network functions and resources. Thisarchitecture benefits a wide range of applications (e.g., servicechaining) and is becoming the dominant form of NFV. Herein below, weintroduce development of NFV under the software-defined NFVarchitecture, with an emphasis on service chaining as its application toBackhaul, Fronthaul and last mile wireless Internet Access. Thesoftware-defined NFV architecture is introduced as the state of the artof NFV and presents relationships between NFV and SDN. Finally,significant challenges and relevant solutions of NFV are described andits application domains (i.e. BH/FH/Access) are discussed.

Current network services rely on proprietary boxes and different networkdevices that are diverse and purpose-built. This situation inducesnetwork management problem, which prevents the operation of serviceadditions and network upgrades (ossification). To address this issue andreduce capital expenditures (CapEx) and operating expenditures (OpEx),virtualization has emerged as an approach to decouple the software fromthe supported hardware and allow network services to be implemented assoftware. ETSI proposed Network Functions Virtualization (NFV) tovirtualize the network functions that were previously carried out bysome proprietary dedicated hardware. By decoupling the network functionsfrom the proprietary hardware boxes, NFV provides flexible provisioningof software-based network functionalities on top of an optimally sharedphysical infrastructure. It addresses the problems of operational costsof managing and controlling these closed and proprietary boxes byleveraging low cost commodity servers.

On the other hand, with the development of Software Defined Networking(SDN), the trend is to integrate SDN with NFV to achieve various networkcontrol and management goals (i.e. dynamic resource management andintelligent service orchestration). Through NFV, SDN is able to create avirtual service environment dynamically for a specific type of servicechain, consequently the dedicated hardware and complex labor work toprovide a new coming service request is avoided. In conjunction with theuse of SDN, NFV further enables real-time and dynamic functionprovisioning along with flexible traffic forwarding.

Software-defined NFV leverages network virtualization and logicallycentralized intelligence to minimize the service providing cost andmaximize the utilization of network resources. In this case, theobtained higher resource utilization will introduce less investigationon the hardware equipment, which on the other hand simplifies networkingoperations. Moreover, by automating current manually intensive networkconfiguration, provisioning, and management, the time and operationalcomplexity are significantly reduced and manual errors are dramaticallydecreased, which offers better scalability. On the other hand,especially in large scale networks, deploying and providing a new kindof service usually results in a long and repeated process that requireslong cycles of validation and testing. By automating the control,management and orchestration, the deployment time and operation costwill be significantly reduced.

Service chaining is the main area of software-defined NFV. In currentnetworks, a service chain includes a set of hardware dedicated networkboxes offering services such as load balancers, firewall, Deep PacketInspection (DPI), Intrusion Detection System (ID S), etc., to support adedicated application. When a new service requirement is added, newhardware devices must be deployed, installed and connected, which isextremely time-consuming, complex, high-cost and error-prone. This kindof networking service requires a dedicate plan of networking changes andoutages, which requires high OpEx. On the other hand, the architectureof software-defined NFV is able to simplify the service chain deploymentand provisioning. It enables easier and cheaper service provisioning inthe local area networks, enterprise networks, data center and Internetservice provider networks, wireless operator networks and theirbackhaul, fronthaul and last mile access networks.

The following introduces the state-of-the-art of NFV and its mainchallenges within the software-defined NFV architecture. Servicechaining is highlighted and discussed as a core application of NFV indifferent contexts. Guidelines are provided for developments of NFV invarious applications to backhaul, fronthaul and last mile access.

Software-Defined Network Function Virtualization

To reduce CapEx and OpEx introduced by diverse proprietary hardwareboxes, NFV exploits and takes advantage of the virtualizationtechnology. NFV allows network operators and service providers toimplement network functions in software, leveraging standard servers andvirtualization technologies, instead of purpose-built hardware. Recenttrends of increased user information demands, explosion of traffic anddiverse service requirements further drive NFV to be integrated withSDN, forming the software-defined NFV architecture. This architectureoffers great flexibility, programmability and automation to theoperators in service provisioning and service modeling.

Diverse and fixed proprietary boxes make the service, deployment andtesting of new systems increasingly difficult. NFV is a key technologyto benefit IT virtualization evolution by separating the hardwarenetwork functions from the underlying hardware boxes by transferringnetwork functions from dedicated hardware to general software running oncommercial off-the-shelf (COTS) equipment, i.e., virtual machines (VMS).These software applications are running on standard IT platforms likehigh-performance switches, service, and storage. Using NFV, thedifferent network functions can be deployed in different locations ofthe networks such as data centers, network nodes, and end-nodes of anetwork edge as required. Currently, the market of NFV includesswitching elements, network elements, network services and applications.A summary of these include:

-   -   Network switching elements, i.e., Broadband Network Gateway        (BNG), carrier grade NAT, Broadband remote access server (BRAS),        and routers.    -   Mobile network devices, i.e., Home Location Register/Home        Subscriber Server (HLR/HSS), Serving GPRS Support NodeMobility        Management Entity (SGSNMME), Gateway support node/Packet Data        Network Gateway (GGSN/PDN-GW), RNC, NodeB and Evolved Node B        (eNodeB) such as that disclosed in T. Wu, L. Rui, A. Xiong,        and S. Guo, “An automation PCI allocation method for eNodeB and        home eNodeB cell,” in Proc. IEEE 6th Int. Conf. Wireless Commun.        Netw. Mobile Comput. (WiCOM), September 2010, pp. 1-4, which is        incorporated herein by reference in its entirety.    -   Virtualized home environments as described in A. Berl, H. de        Meer, H. Hlavacs, and T. Treutner, “Virtualization in        energy-efficient future home environments,” IEEE Commun. Mag.,        vol. 47, no. 12, pp. 62-67, December 2009 and R. Mortier et al.,        “Control and understanding: Owning your home net-work,” in Proc.        IEEE 4th Int. Conf. Commun. Syst. Netw. (COMSNETS), January        2012, pp. 1-10, each of which are incorporated herein by        reference in its entirety.    -   Tunneling gateway devices, i.e., IPSec/SSL virtual private        network gateways.    -   Traffic analysis elements, i.e., Deep Packet Inspection (DPI),        Quality of Experience (QoE) measurement.    -   Service Assurance, Service Level Agreement (SLA) monitoring,        Test and Diagnostics such as that described in H. Ludwig et al.,        “Web service level agreement (WSLA) language specification,” IBM        Corp., New York, N.Y., USA, Tech. Rep., 2003, pp. 815-824, which        is incorporated herein by reference.    -   Next-Generation Networks (NGN) signaling such as Session Border        Controller (SBCs), IP Multimedia Sub-system (IMS).    -   Application-level optimization devices, i.e., Content Delivery        Network (CDNs), load balancers, cache nodes, and application        accelerators such as that described in F. T. Leighton and D. M.        Lewin, “Content delivery network using edge-of-network servers        for providing content delivery to a set of participating content        providers,” U.S. Pat. No. 6,553,413, Apr. 22, 2003, which is        incorporated herein by reference in its entirety.    -   Network security devices, i.e., Firewalls, intrusion detection        systems, DOS attack detector, virus scanners, spam protection,        etc. such as that described in E. D. Zwicky, S. Cooper,        and D. B. Chapman, Building Internet Firewalls, Sebastopol,        Calif., USA: O'Reilly Media, 2000, which is incorporated herein        by reference in its entirety.

The major advantage of using NFV is to reduce middle dedicated hardwareboxes deployed in the traditional networks to take the advantages ofcost savings and bring flexibility. On the other side, NFV technologyalso supports the co-existence of multi-tenancy of network and servicefunctions, through allowing the usage of one physical platform fordifferent services, applications and tenants.

NFV Framework

ETSI defines the NFV architectural framework 302 as illustrated in FIG.3 enabling virtualized network functions (VNF) 304 to be deployed andexecuted on a Network Functions Virtualization Infrastructure (NFVI)306, which consists of commodity servers 307 to provide computing,storage and network functionalities wrapped with a software layer thatlogically partitions them. Above the hypervisor layer, a VNF 304 istypically mapped to one VM (virtual machine) 309 in the NFVI. Thedeployment, execution and operation of VNFs 304 on the NFVI 306 aresteered by a Management and Orchestration (M&O) system 308, whosebehavior is driven by a set of metadata describing the characteristicsof the network services and their constituent VNFs. The M&O systemincludes an NFV Orchestrator 310 in charge of the lifecycle of networkservices, a set of VNF managers 312 in charge of the life cycle of theVNFs and a virtualized infrastructure manager 314, which can be viewedas an extended cloud management system responsible for controlling andmanaging NFVI resources.

Software-Defined Networks

A Software-Defined Network (SDN) is an important and recently emergingnetwork architecture to decouple the network control from the dataforwarding. With its inherent decoupling of the control plane from thedata plane, SDN offers a greater control of a network throughprogramming. This combined feature would bring potential benefits ofenhanced configuration, improved performance, and encourages innovationin network architecture and operations. Especially, SDN offers apromising alternative for traffic steering by programmaticallyconfiguring forwarding rules as described in N. Handigol, S.Seetharaman, M. Flajslik, N. McKeown, and R. Johari, “Plug-n-serve:Load-balancing Web traffic using OpenFlow,” in Proc. ACM SIGCOMM Demo,2009, pp. 1-2, which is incorporated herein by reference in itsentirety.

FIG. 4 depicts the SDN architecture. There are three different layers.The application layer 402 covers an array of applications 404 focusingon network services, and they are mainly software applicationscommunicating with the control layer 406. As the core of SDN, thecontrol layer 406 consists of a centralized controller 408, whichlogically maintains a global and dynamic network view, takes requestsfrom the application layer 402, and manages the network devices viastandard protocols 409 using control policies 410. Communicationsbetween the applications layer 402 and the control layer 406 occurthrough application program interfaces 412. The data-plane layer 414provides infrastructure including switches, routers and networkappliances through physical switches 416, virtual switches 418 andnetwork devices 420. In an SDN context, these devices are programmableand support standard interfaces. Communications between the controllayer 406 and the data plane layer 414 occur via application programinterfaces 422.

The application layer 402 utilizes the northbound APIs 412 tocommunicate with the SDN controller 406 (Control Plane Layer), whichenable different control mechanisms for the networks. The southboundAPIs 422 define the communication interface between the controller layer406 and data plane devices within the data plane layer 414, which enablethe application to control the forwarding device is a flexible andprogrammable manner.

NFV Versus SDN

NFV and SDN are closely related and highly complementary to each other.NFV can serve SDN by virtualizing the SDN controller 406 (which can beregarded as a network function) to run on the cloud, thus allows dynamicmigration of the controllers to the optimal locations. In turn, SDNserves NFV by providing programmable network connectivity betweenvirtual network functions (VNFs) to achieve optimized trafficengineering and steering. However, NFV and SDN are completely differentfrom the concepts to the system architecture and functions, which aresummarized by the following aspects.

NFV is a concept of implementing network functions in software manner,while SDN is concept of achieving centrally controlled and programmablenetwork architecture to provide better connectivity. NFV aims atreducing CapEx, OpEx, and space and power consumption, while SDN aims atproviding network abstractions to enable flexible network control,configuration and fast innovation. NFV decouples the network functionsfrom the proprietary hardware to achieve agile provisioning anddeployment, while SDN decouples the network control plane from the data

Software-Defined NFV Architecture

The software-defined NFV system is illustrated in FIG. 5. The systemconsists of a control module 502, forwarding devices 504 and NFVplatform 506 at the edge of the network. The logic of packet forwardingis determined by the SDN controller 508 and is implemented in theforwarding devices 504 through forwarding tables. Efficient protocols,e.g., OpenFlow, can be utilized as standardized interfaces incommunicating between the centralized controller 502 and distributedforwarding devices 504. The NFV platform 506 leverages commodity servers510 to implement high bandwidth NFs (network functions) at low cost.Hypervisors 512 run on the servers 510 to support the VMs 513 thatimplement the NFs. This platform 506 allows customizable andprogrammable data plane processing functions such as middle box offirewalls, IDSs, proxies, which are running as software within virtualmachines, where NFs are delivered to the network operator as pieces ofpure software.

The SDN controller 508 and the NFV orchestration system 514 compose thelogical control module 502. The NFV orchestration system 514 is incharge of provisioning for virtualized network functions 516, and iscontrolled by the SDN controller 508 through standard interfaces 518.Referring now to FIG. 6, there is illustrated a process for provisioningfunctions. After obtaining the network topology and policy requirementsat step 602, the control module 508 computes the optimal functionassignments (assigning network functions to certain VMs) at step 604 andtranslates at step 606 the logic policy specifications into optimizedrouting paths. The function assignments are enforced at step 608 by theNFV orchestration system 514, and the controller 508 steers the traffictraveling through the required and appropriate sequence of VMs 513 andforwarding devices 504 by installing forwarding rules into them at step610.

From Middle Box to NFV

Though NFV is not limited to virtualizing middle boxes, the concept ofNFV was initiated in the context of middle box. The present disclosureintroduces the evolution from a traditional purpose-built middle box toNFV, during which consolidated middle box and software-defined middlebox act as transitional paradigms.

Middlebox Overview

A middle box is a networking forwarding or processing device thattransmits, transforms, filters, inspects or controls network traffic forpurposes of network control and management. A middle box service orfunction is a method or operation performed by a network device thatneeds specific intelligence about the applications. Typical examples ofmiddle boxes include network address translators (NATs) that modifypacket's destination and source addresses, and firewalls that filterunwanted or malicious traffic. The following are commonly deployedmiddle boxes:

-   -   1) Network Address Translator (NAT)    -   2) Firewall (FW)    -   3) Intrusion Detection System (IDS)    -   4) Load Balancer (LB)    -   5) WAN Optimizer    -   6) Flow Monitor (FM)        Consolidated Middlebox

Here, an overview for the efforts on consolidating middle boxes isprovided, which are precursors to the current NFV paradigm.

-   -   1) CoMb    -   2) APLOMB    -   3) Integrate Middle Boxes into Network        Software-Defined Middlebox

As SDN evolves, the principles of abstracting the architecture layer ofnetwork from the control plane 406 and data plane 414 have beeninvestigated in various contexts. This idea introduces some uniqueopportunities for the development of middle boxes. Inspired by the ideaof SDN, some researchers proposed a software-defined middle box andcorresponding networking architecture, with the aim of providingfine-grained and programmable control over the middle box state andnetwork forwarding.

Service Chaining

Service chaining is an important model for network service providers, inwhich NFV plays an important role. It is utilized to organize theservice function deployment, where the ability of specifying an orderedlist of service processing for the service's traffic flows is provided.A service chain defines the required processing or functions and thecorresponding order that should be applied to the data flow. Thesechains require the integration of service policy and the aboveapplications to achieve optimal resource utilization.

Traditional service chaining mainly relies on manual configuration whichis tedious, error-prone and clumsy. SDN provides new capabilities tosteer traffic dynamically based on user requirements. However,hardware-based middle boxes limit the benefit of SDN due to their fixedfunctionalities and deployment. NFV is a good enabler for SDN. With theability of dynamic function provisioning offered by NFV and thecentralized control of SDN, new opportunities emerged in servicechaining. Better performance and resource utilization can be achievedwith the software-defined NFV architecture.

SDN & Middle Box Based Service Chaining

SDN offers the flexible control approach and enables dynamic trafficforwarding, and this style of traffic control for middle box-specificflow can realize flexible and efficient service chaining with no need togenerate any placement or introduce some constraints on middle boxes,which are on the other hand easily supported by current SDN standards.The following are some of the important functions:

-   -   1) Symple    -   2) Steering    -   3) Flowtag        Service Chaining in the Software-Defined NFV Architecture

SDN and NFV together have the potential to benefit service operators,satisfy user service level agreements and accurately monitor and controlnetwork traffic, which further reduces and minimizes the operating cost.On one hand, NFV moves network functions out of dedicated hardware boxesto the software based on general hardware platform. SDN moves controlfunctions out of the hardware and places it in the software controller.Therefore, the service deployment and service chains can be provided andreconfigured in the controller. In this way, not only flexible anddynamic operations are allowed, the chance for operation error andevents will be much smaller because the network controller has anoverall view, which reduces the probability of inconsistentconfigurations.

Moving the required network functions into software means that deployingthe service chain no longer requires acquiring a dedicated middle box.In this case, the network functions execute as the software running onvirtual machines with the control of a hypervisor 512, which enableflexible computational and networking resource provisioning. Thus, sincethe computational capacity can be increased when required, there's noneed to over-provision. On the other hand, software-defined NFV servicechaining also helps the network upgrade process. For geographicallydistributed networks, upgrading network devices is costly. Moreover, theerrors in the network updates and re-configuration can bring down theentire network. However, with the software-defined NFV, serviceproviders are able to create new chains without radically changinghardware. Finally, service operator can utilize these service chainingtechniques by themselves, instead of using third party providers. Withintelligent service chaining, complexity of resource provisioning issignificantly reduced. Thus, service providers can deliver services ondemand without the help of third parties.

FIG. 7 illustrates an example of the service chaining process. Within asoftware-defined NFV architecture, a unified control and orchestrationframework 502 is required to integrate the SDN controller 508,forwarding elements 702 and virtual network functions 573. Moreover, dueto the existence of dynamic function and resource provisioning, thisframework should also provide coordinated control of both networkforwarding state and network functions states. Taking user policies 704as inputs, the control module 502 assigns the NFs 706 fulfilling theseservices in an optimal way and meanwhile the optimal routing paths 708of all policies are selected taking account of the resource constraints.The service functions 710 are then chained by the centralized controllerand the traffic flows 712 are steered according to the service chains.

Challenges and Problems of Network Function Virtualization

NFV is an important innovation and a promising approach for the serviceoperators and providers. However, it also faces several challenges. Herethe corresponding challenges, open problems, and related solutions aresummarized with the classifications organized in Table 1.

Function Virtualization

The virtualized functions should meet performance requirements tosupport packet processing at line-rate for multiple tenants. First,since neither the hypervisors 512 nor the virtual machines 573 have beenoptimized for the processing of the middle box, obtaining highperformance, i.e., high I/O speed, fast packet processing, shorttransmission delays, etc. from standard servers is the main challengefor function virtualization. Further, as a server may implement a largeamount of functionality, their platforms should host a wide range ofvirtual machine 513 and software packages. Finally, NFV hardware andsoftware platforms should support multi-tenancy, because they areconcurrently run by software belonging to the different operators. Theseco-located VNFs 304 should be isolated not only from a security but alsoa performance point of view. Here is a summary of some important relatedworks on function virtualization.

-   -   1) DPDK is a set of libraries and drivers for fast packet        processing for the network functions. DPDK can be run on a wide        range of processors. However, the DPDK system has some        limitation to support virtualization as it cannot support        flexible, high performance functionality in the NFV environment.    -   2) NetVM is a software platform for running diversity network        functionality at line-speed based on the general commodity        hardware. It takes advantage of DPDK's high throughput packet        processing capabilities, and further enables flexible traffic        steering and overcomes the performance limitations of hardware        switching. Thus, NetVM provides the capability to support        network function chains by flexible, high-performance network        elements.    -   3) ClickOS is a high-performance, virtualized software network        function platform. It provides small, quickly booting, and        little delay virtual machines, and over one hundred of them can        be concurrently run while guaranteeing performance on a general        commodity server. To achieve high performance, ClickOS relies an        extensive overhaul of Xen's I/O subsystem to speed up the        networking process in middle boxes. ClickOS is proof that        software solutions alone are enough to significantly speed up        virtual machine processing, to the point where the remaining        overheads are dwarfed by the ability to safely consolidate        heterogeneous middle box processing onto the same hardware.        Portability

The NFV framework is expected to support the loading, executing andmoving of VNFs 304 across different but standard servers in multi-vendorenvironments. This capability is known as portability. These virtualizednetwork functions defeat the portability goal and key benefits of NFV,namely the capability of multi-tenancy and resource isolation. Theportability challenge is how to achieve high performance leveraginghardware accelerators and at the same time have hardware independentNFs. This approach ensures that the VNFs 304 are OS-independent andresource isolation is also guaranteed since the VNFs 304 are executed onindependent VMs and are decoupled from the underlying OS by thehypervisorlayer.

Standard Interfaces

NFV relies on existing infrastructure to touch the customer. In thiscase, it is also highly unlikely that an upgrade of the physical networkor entire operational support systems will be feasible. This is amanagement software integration challenge with the interfaces betweenNFV and underlying infrastructure. On the other hand, the interfacesbetween the centralized controller and VNFs 304 should also bestandardized. To smoothly bridge NFV with upper and lower layers, theVNFs 304 and the underlying computing platform should be described bystandard templates that enable flexible control and management. Thus,north- and south-bound interface APIs 412, 422 need to be developed.North-bound interface 412 interactions are used to control and managefunctions to different types of instances, e.g., physical servers, VM513 and VNFs 304. Since network functions need service-oriented APIs tobe controlled directly or indirectly, each network service has aspecific operation policy and SLA. Moreover, VNFs 304 could use thenorth-bound API 412 for the requests. On the other hand, the south-boundAPIs 422 are utilized to communicate with the NFVI 306 and requestinformation from other framework entities. Thus, how to design aflexible and efficient API for both the north-bound and south-boundcommunications are important problems in the research and development ofNFV technologies.

Function Deployment

Fine-grained deployment, control and management of network functions areneeded in the context of NFV-enabled network nodes, for variousoptimization purposes. Thus, many challenges are related to algorithmand system design of function deployment.

One of these challenges is to automatically provide network and functionprocess resources according to the usage of the resources involved. Asimilar and probably even more important challenge is to achieveautomatic placement and allocation of the VNFs 304, since the placementand assignment of the VNFs 304 significantly impact the performance ofservice chaining. Both automated provisioning and placement require aglobal view of the resources and a unified control and optimizationsystem with various optimization engines running in it. Another issue isto translate higher-level policies, which are generated from theresource allocation and optimization mechanisms, into lower levelconfigurations. Templates and standards should be developed to guaranteeautomated and consistent translation. For example, when there is a needto achieve a high-level goal of reducing the networking transmissiondelay, the optimization engine may require an algorithm to provision andplace virtual functions ensuring that the least overall transmissiondelay is achieved. Conversely, when it is required to achieve theminimum or maximum link utilization, it would need a differentoptimization engine with a different algorithm. For more effectiveoperation and control, the optimization approach should supportreal-time swap to make provisioning and placements that dynamicallymatch the high-level policies from the operator and application.

Traffic Steering

SDN offers the new agility of traffic steering by allowing the networkoperators and service providers to specify a logical control policy, andthen automatically translates this into data plane 414 forwarding rules.Prior to this, the routing paths are carefully selected by theoptimization framework taking into account the physical topology, linkcapacities, and network resource constraints. Solid work has been doneon traffic steering in hardware based middle box systems. However, inthe software-defined NFV architecture, traffic steering is jointlyoptimized with NFV deployment that can achieve better composition.However, the unified optimization paradigm also makes the optimizationproblem difficult to solve since more variables are introduced. Toachieve online computing of traffic steering, heuristic algorithmsshould be designed to reduce the computing complexity.

TABLE 1 Challenges Description Solution Function VirtualizationVirtualized functions should meet certain Important related works:requirements to support packet processing at (1) DPDK, a set oflibraries for fast packet line-rate: processing. (1) High performance(high I/O speed, (2) NetVM, a system for running network fast packetprocessing, short transmission functionality and middlebox at line-speedin delays, etc.) general commodity hardware. (2) Support multi-tenancy(3) ClickOS, a small, quick-boot, low-delay, (3) OS-independentvirtualized software midcllebox platform. Portability The NFV frameworkis expected to load, Deploying network functions via a virtual executeand move VNFs across different but software environment enhances theportability. standard servers in multi-vendor This approach ensures thatthe VNFs are OS- environments. This capability is known as independentand resource isolation is also portability. guaranteed. StandardInterfaces Standardized API should be developed to Both VNFs andcomputing resources are enable NFV to reach the customers via describedvia standard templates. Normalized underlying infrastructure and to becentrally north- and south-bound should be developed controlled andmanaged. between these layers. Function Deployment Fine-graineddeployment, control and A monitoring system collecting and reporting onmanagement of network functions, are the behavior of the resources, anda unified needed in the context of NFV-enabled control and optimizationsystem with various network nodes, for various optimization optimizationengines should be developed. purposes. Traffic Steering In thesoftware-defind NFV architecture, To achieve online computing of trafficsteering, traffic steering should be jointly optimized heuristicalgorithms should be designed to reduce with function deployment, makingthe the computing complexity. optimization problem difficult to solve.Applications

Software-defined NFV technology is useD for delivering significantbenefits in niche applications today, while its full scale use andbenefits have yet to be achieved. The following describes the majordomains that will dominate the software-defined NFV scenario over nextfew years.

Cloud-Computing

Cloud computing enables globally distributed services and enterprises toquickly deploy, manage and optimize their computing infrastructuredynamically. Partitioning or replicating a service across multipleglobally distributed instances allow these services to move closer tothe users thus providing richer user experiences, avoid infrastructurebottlenecks, and implement fault tolerance.

NFV is an enabler of such dynamic service provisioning. By replacingservice elements with virtual network functions, new functions can beadded or improved by updating a software image, rather than waiting fora vendor to develop and manufacture a dedicated box. Furthermore, whileintegrated with SDN, service providers can express and enforceapplication traffic management policies and application deliveryconstraints at the required level of granularity.

NFV allows service providers to provide better services to the users bydynamically changing their deployment topologies or traffic allocationsbased on user access patterns, user consumption and mobility,infrastructure load characteristics, infrastructure failures and manysuch situations that may cause service degradation, disruption or churn.Similarly, replicated service instances might need to bemoved/instantiated/released to mask infrastructure failures, loadconditions, or optimize the deployment based on consumption patterns andsocial interaction graphs. NFV can also provide intelligentinfrastructure support for such dynamic service deployment scenarios.Moreover, since NFV offers good support for multi-tenant usage, it isavailable for wide area dynamic multi-cloud environments that can beshared by multiple providers to implement their specific distributedservice delivery contexts.

Below are summarized some important works trying to implement NFV inclouds:

-   -   1) CloudNFV    -   2) THE REALTIME CLOUD    -   3) CLOUDBAND        Mobile Network

NFV considers all network functions for virtualization throughwell-defined standards, i.e., in mobile network, NFV targets atvirtualizing mobile core network and the mobile-network base station.NFV also benefits data centers owned by mobile service providers,including mobile core network, access networks and mobile cloudnetworks.

For the core networks, which are the most important part of mobilenetworks, NFV allows the cellular providers to adopt a network more akinto the data centers, which consist of simple forwarding devices 504,with most functionality executed in commodity servers that are close tothe base stations. Some network functions can even be fulfilled bypacket-processing rules installed directly in the switches. In thesystem, a logically centralized controller is able to steer the networktraffic through the required network functions to realize servicechaining.

For the access networks, the base stations are being virtualized aswell. Thus, SDN and NFV are applied to the wireless access networks tosharing their remote basestation infrastructure to achieve bettercoverage and services with the minimum investment of CapEx and OpEx.

Enterprise Network

NFV is also being utilized in the enterprise network. Network managerswould like to consume as much or as little of the network as they need,but there is a gap between what enterprise customers want and whatservice providers can offer today, which can be address by NFV. Itenables the dynamic provisioning of virtual network services oncommodity servers within minutes instead of months.

NFV for the enterprise will require their platform to become morecomfortable embracing software L4-7 services, as well as changes intheir operation models. An understanding of how to optimize performancewith DPDKs, and potentially even looking at programmable hardware iscritical. Another challenge is the time and process it takes tore-architect monolithic services that were predominantly deployed fornorth-south traffic.

A comprehensive overview of NFV within the software-defined NFVarchitecture is provided. NFV and its relationship with SDN has beenintroduced. The evolution of NFV has been reviewed and the discussionhas covered how middle boxes evolved to virtual network functions. Inparticular, service chaining as a typical application of NFV has beendescribed. Furthermore, software defined NFV challenges and possiblesolutions were covered. Next, a discussion of how to take the SDN andNFV concepts and leverage them in planning, designing and implementing awireless backhaul, fronthaul and last mile access networks usingstandard based protocols as well as open source protocols will beprovided.

Access and backhaul networks need to carry significantly more data inorder to support ever growing data use within networks which calls fornetwork densification. However, as illustrated in FIG. 8, when manysmall cells 802 are densely deployed within a small cell network 804,the backhaul network 806 may become a bottleneck due to the issues withproviding a wireline link 808 between each cell 802 in the backhaulnetwork 806 due to the large number of wireline connections within anetwork. The backhaul network 806 then further provides interconnectionto the core network 810 for passing messages to and from the small cellnetwork 804.

Referring now to FIG. 9, there is illustrated an implementation of awireless small cell network 902. The small cell wireless backhaulnetwork 902 is needed due to its multi-hop operation and ability tooperate in multiple bands (mmWave bands, Sub 6 GHz bands and free spaceoptical (FSO) bands. The small cell network 902 provides a plurality ofwireless connections 904 between the cells 906 and the backhaul network908. The backhaul network 908 then forwards messages received on thewireless communications links 904 to/from the core network 910.

Referring now also to FIG. 10, there is illustrated the manner toutilize an SDN-based system for creating the connections with the smallcell network 902. An SDN controller 1002 enables connections to a numberof different small cell backhaul nodes 1004. The SDN controller 902 isbased on OpenDaylight and controls adaptively powering on/off smallcells 1004 and reconfigures the backhaul forwarding topology accordingto traffic demands. OpenDaylight is a collaborative open source projecthosted by the Linux foundation. OpenDaylight promotes software definednetworking (SDN) and network function virtualization (NFV). OpenDaylightsoftware is written in the Java programming language. OpenDaylightsupports technologies such as OpenFlow. OpenDaylight is a modular openplatform for customizing and automating networks of any size and scale.OpenDaylight is driven by a global, collaborative community of vendorand user organizations.

The core of the OpenDaylight platform is the Model-Driven ServiceAbstraction Layer (MD-SAL). In OpenDaylight, underlying network devicesand network applications are all represented as objects, or models,whose interactions are processed within the SAL. The SAL is a dataexchange and adaptation mechanism between data models representingnetwork devices and applications. The data models provide generalizeddescriptions of a device or application's capabilities without requiringeither to know the specific implementation details of the other. Withinthe SAL, models are simply defined by their respective roles in a giveninteraction.

The OpenDaylight platform is designed to allow downstream users andsolution providers maximum flexibility in building a controller to fittheir needs. The modular design of the OpenDaylight platform allowsanyone in the OpenDaylight ecosystem to leverage services created byothers; to write and incorporate their own; and to share their work withothers. OpenDaylight includes support for the broadest set of protocolsin any SDN platform—OpenFlow, OVSDB, NETCONF, BGP and many more—thatimprove programmability of modern networks and solve a range of userneeds.

The SDN controller 902 uses an optimizer module 1006 that is configuredwith different policies in order to minimize the power and latency andmaximize system capacity. The optimizer module 1006 uses SDN for theoperation and management of small cell wireless networks to extend theOpenFlow protocol in order to gather wireless and power consumptionstatistics, which are exchange between the controller 1002 and smallcell backhaul nodes 1004 using and an LTE out of band control channel1008. OpenFlow is a communication protocol that provides access to theforwarding plane of the network switch or router over the network.OpenFlow enables network controllers to determine the path of networkpackets across a network of switches. The controllers are distinct fromthe switches. The separation of the controller from the forwardingallows for more sophisticated traffic management than is feasible usingaccess control lists and routing protocols. Also, OpenFlow allowswitches from different vendors to be managed remotely using a single,open protocol. OpenFlow is an enabler of software defined networking.

OpenFlow allows for the remote administration of a layer 3 switch'spacket forwarding tables, by adding, modifying and removing packetmatching roles in action. Routing decisions can be made periodically orad hoc by the controller and translated into rules and actions with aconfigurable lifespan, which are deployed to a switch's flow table,leaving the actual forwarding of matched packets to the switch at wirespeed for the duration of those rules. Packets which are unmatched bythe switch can be forwarded to the controller. The controller decides tomodify existing flow table rules on one or more switches or to deploynew rules, to prevent a structural flow of traffic between switch andcontroller. It could even be decided to forward the traffic itself,provided that it is told the switch to forward entire packets instead ofjust the header. The OpenFlow protocol is layered on top of thetransmission control protocol and proscribes the use of transport layersecurity.

Referring now to FIG. 11, there is illustrated a heterogeneous network(HetNet) 1102. In a HetNet, a dense small cell network 1102 comprised ofa number of small cell nodes 1004 that coexist with an overlay of LTEeNBs 1104 providing the basic coverage. In such a deployment, trafficfrom user equipments (UE) 1106 are forwarded from the small cell node1104 over multiple wireless backhaul links 1108 to a gateway node 1110,which is typically co-located at the eNBs 1104. Thus, in a multi-hopdeployment, routing and forwarding are crucial aspects to consider,since they have to dynamically power on and off nodes 1004, according totraffic demand changes creating a liquid wireless backhaul were networkresources are used where they are needed. Multi-hop deployment is usedfor routing and forwarding of the data plan over a multiband (mmWave,sub 6 GHz and FSO) network.

With software defined networking (SDN), packet forwarding can be handledby a centralized controller 1002 (FIG. 10), in a flexible and effectiveway. Adding device configuration capabilities for this kind ofarchitecture allows small cell wireless networks to be fully managed. Ina typical SDN-based architecture, the SDN controller 1002 sends OpenFlowmessages that must be routed over the wireless links 1008 towards the1004. This can lead to potentially long latency.

An SDN-based network architecture for small cell backhaul operation andmanagement is proposed for dealing with these latency issues. Referringnow to FIG. 12, based on the HetNets concept, the proposed SDNcontroller 1202 transmits an OpenFlow messages 1204 via LTE controlchannels 1206 directly to small cell nodes 1208. Extensions to theOpenDaylight (ODL) controller 1210 provide the necessary resilientrouting infrastructure for a small cell backhaul operation. A backhaulorchestrator 1212 dynamically optimizes the small cell backhaul byminimizing power and latency while maximizing the capacity of thebackhaul network.

Referring now also to FIG. 13, there is illustrated a more detaileddescription of a backhaul network KPI (key performance indicator) 1302.The backhaul network KPI 1302 is implemented within the SDN controller1202 to enable communications between the SDN controller and small cellswithin the small cell backhaul network. As mentioned previously, theOpenDaylight controller 1210 provides routing infrastructure for thesmall cell backhaul operation. The OpenDaylight controller 1210 utilizesan application program interface 1304 for enabling communicationsbetween the controller 1210 and a backhaul orchestrator 1212. Thebackhaul orchestrator 1212 dynamically optimizes the small cell backhaulby minimizing power and latency while maximizing the capacity of thebackhaul network. The backhaul network KPI 1302 must maintain acommunication channel 1206 with the SDN controller 1304 in order to beable to exchange control plane messages with the small cell nodes 1208.This communication channel 1206 can be established in the same networkinterface as the one used for the data plane (in-band connectivity) orin a different interface (out-of-band). With in-band connectivity, theinfrastructure costs are reduced, but if link failure occurs, the nodeloses the connection with the controller 1210. Out-of-band control planeconnectivity requires an additional NIC (network interface controller)in the managed devices. An LTE interface 1210 is used on each SDNenabled small cell backhaul node 1310 for SDN control planeconnectivity, in order to provide a robust channel and reduce SDNcontrol latency while the data plane is using the multi-hop backhaulconnectivity over a multiband (mmWave, sub 6 GHz and FSO) network.

Small cell wireless backhaul links may have dynamic link outages,especially when operating at mmWave band. A link can temporarily go fromnon-line of sight to outage (e.g. due to blockage), leading to changesin the backhaul topology and consequently, in the available capacity.When such events happen, the SDN controller 1202 can perform pathrecalculation between the backhaul small cell nodes 1208 but the processmay take a significant amount of time. The backhaul network KPI 1302 asillustrated in FIG. 13 uses fast failover (FF) group tables 1306 fromthe OpenFlow plug-in 1308 to rapidly repair link failures locally.

The backhaul orchestrator 1212 communicates with the multidimensionaloptimizer 1310. The Orchestrator Interface 1304 is used to communicatewith the backhaul orchestrator 1212 in order to perform thereconfiguration of the small cell backhaul network. Also, thisconfiguration can be triggered by the backhaul orchestrator 1212 throughthis REST API. The new configurations are pushed to the wirelesscommunications services (WCS) and new paths are requested to the PathCalculator. The multidimensional optimizer 1310 finds a maximum valuebased upon latency, capacity and 1/power using Euler-Lagrangemultipliers. The backhaul network KPI 1302 further includes a packetinspection/handling module 1312. The packet inspection/handling module1312 inspects and controls the data packets that are transmitted overthe communications channels 1203 to the small cell nodes 1208. Thepacket inspection/handling module 1312 parses packets sent to the SDNcontroller 1202 (e.g. for new flows when no rules are installed at thesmall cell backhaul nodes 1208). The extracted information is sent tothe path calculator 1314, which replies with a primary path from thesource to the destination node according to a given path calculationstrategy. The original packet is then sent back to the destination node.

The path calculator 1314 is responsible for calculating alternate pathsto the small cell nodes 1208 when existing links fail. The pathcalculator 1314 computes paths between the powered on small cellbackhaul nodes 1208 and instructs the installation of new forwardingrules. The path calculator 1314 uses a network graph that contains onlythe active nodes. If the fast failover (FF) strategy is active, amaximum disjoint path is also calculated from each intermediate node,and the required forwarding rules are installed in combination with theusage of the FF group table 1306 feature from OpenFlow. The link/pathprocessing calculation module 1314 uses information from the neighborlist 1316 to make the new path calculations. The neighborhood mapper1316 is a database list of small cell nodes and their associatedneighboring nodes. The neighborhood mapper 1316 infers the neighborhoodand interference graph for each node/link from the existing topology.Small cell backhaul nodes 1208 send out periodic beacons to neighbors.The collected information statistics are sent to the SDN controller 1202and used to augment existing data from the backhaul links

The OpenFlow plug-in 1308 includes an OpenFlow detection module 1318 fordetecting OpenFlow messages. The flow process module 1320 calculates themessage routing. The wireless configuration service 1322 sends wirelessspecific configuration requests to the managed small cell backhaul nodes1208 through an OpenFlow protocol extension. The Wireless StatisticsManager 1328 collects wireless related statistics from the managed smallcell backhaul nodes 1208 over an aggregator API 1330 through anextension of the statistics manager component 1324 from the OpenFlowPlugin 1308. The statistical information is fed to the statistics module1324 from the small cell nodes 1208. The requests and statistics canhave different types, which are specified by a bit mask field in therequest body. Each of the modules within the OpenFlow plugin 1308communicates with the small cell nodes 1208 through an OpenFlow API1326. A metrics collector 1328 is responsible for obtaining networkperformance metrics that cannot be directly retrieved through OpenFlowplug-in 1308. The metrics are obtained through the aggregator API 1330.The calculated data is merged into the available statistics and can beused by every other SDN controller 1202 component.

Referring now to FIG. 14, there is illustrated a flow diagram of theprocess for link repair. Upon occurrence of a link failure at step 1402a disjoint backup path toward the gateway node 1110 at each small cellbackhaul node 1004 is calculated at step 1404 using the fast failovergroup tables 1306. If the failure that triggered the usage of adifferent network path persists, as determined at inquiry step 1408, thecontroller 1302 week calculates new routes at step 1410 based upon thecurrent apology and previously calculated energy optimizationstrategies. Control then passes back to inquiry step 1408 to determineif the failure persists. When the failures do not persist, the processis completed at step 1402.

With SDN it is possible to have flexible path calculation strategies acton detailed forwarding decisions. For multi-hop small cell backhaulnetworks, it will be essential to control the existing paths latency.This requires an estimation of the delay for each link and path at theSDN controller 1202 which can also depend on existing queuing strategiesto implement control of existing paths' latency. Therefore, some flowsmight be routed along low latency paths, while others are routed tohigher latency paths with higher capacity. New routing algorithms mightbe needed, allowing fast path calculation while supporting multipleconstraints (bandwidth, latency, capacity and power). Therefore, theSDN-based network would manage flow rules, wireless link and ourmanagement parameters. The SDN based network interacts with a backhaulorchestrator 1212, responsible for optimizing the backhaul networkoperation.

Due to the increasing traffic demand, existing mobile access andbackhaul networks face a capacity problem. In order to increase thecapacity, it is customary to deploy many small cells which may bedynamically controlled based upon traffic demand as illustrated in FIG.15. The small cell backhaul network 1502, as described previously,consist of a plurality of individual small cell nodes 1504 that areinterconnected via communication links 1506. Each of the small cellnodes 1504 are interconnected with each of the small cell nodes withinits vicinity via one of the communication links. Thus, for example asillustrated in FIG. 15 node 1504 x is interconnected with each of thesurrounding nodes 1504 y (in this case eight nodes) through anassociated communication link 1506. Thus, node 1504 x can communicateover the small cell backhaul network 1502 through any of the adjacentsmall cell network nodes 1504 y.

As a consequence, the backhaul fabric for small cell networks 1502 needsto cope with the massive increase in user demands since the laying offiber to each small cell node 1504 is not economically feasible. It ispossible to have mmWave based mobile backhaul networks due to the largechunk of spectrum that is available both in unlicensed bands (the 60 GHzand 70/80 GHz bands) as well as licensed bands of 24, 28 and 39 GHz.However, due to the specific propagation characteristics of the mmWavespectrum, communications links 1506 between small cell nodes 1504 mayface challenging network outages. Additionally, a more flexible designof the backhaul network 1502 is desired in order to cope with thediversification of service requirements.

A small cell backhaul network architecture based on the concept ofsoftware defined networking will be able to address these issues andprovide a mmWave based mobile backhaul network. Referring now to FIG.16, in order to cope with the dynamics of mmWave, the SDN control planemakes forwarding decisions inside the backhaul by calculating for eachsmall cell node 1602 a backhaul primary link 1604 and a set of backuplinks 1606. The set of backup links 1606 include at least one backuplink which may be utilized if the primary link 1604 goes out. UsingOpenFlow Fast Failover groups such as those described herein above, afast local repair of a mmWave backhaul link 1506 or other transmissiontype links whenever local problems such as link outages are detected canbe achieved leading to a resilient backhaul mesh architecture. Theproposed architecture leads to a lower packet loss and consequentlyhigher throughput data rate and better network reliability.

Referring now to FIG. 17, network reliability may also be improvedutilizing an architecture wherein each node 1702 uses SDN-based channelestimation to multiplex between line of sight (LOS) mmWaves, non-line ofsight (NLOS) sub-6 GHz and free space optics (FSO) transmissions. Thisis achieved using a LOS mmWave transceiver 1704 for transmitting line ofsight millimeter waves 1706, an NLOS transceiver 1708 for transmittingnon-line of sight sub-6 GHz signals 1710 and a FSO transceiver 1712 fortransmitting FSO signals 1714. Multiplexing control circuitry 1716multiplexes between the LOS mmWave transceiver 1704, an NLOS transceiver1708 and an FSO transceiver 1712 based upon the environmental and systemoperating conditions. When the atmospheric conditions are good, thenetwork relies upon the FSO transceiver 1712. When atmosphericconditions become foggy or rainy, the system adaptively switches to RFLOS transceiver 1708 or the LOS transceiver 1704 using the multiplexercontrol 1716. If the operating environment has many physical obstaclesbetween the transmitter and the receiver, the system would select theNLOS transceiver 1708.

Despite introducing new technologies at lower layers of the protocolsuch as better modulation and coding schemes or coordinating multipointtransmissions, the predicted demand is much higher than what can besupported with new physical layer only technologies in the short term. Acommon assumption to provide increased capacity at scale is to use ahigher frequency band were more spectrum is available and to reduce thecell size in order to increase spatial reuse. Backhaul operation isoften dominated by proprietary solutions which hinder innovation. Animportant challenge to solve for small cell backhaul links is anefficient but flexible forwarding architecture which relays user dataover a multi-hop wireless backhaul between a plurality of small cellnodes.

Referring now to FIG. 18, in a typical SDN-based architecture, acentralized controller 1802 installs within small cell nodes flexiblerules 1804 that determine the forwarding behavior within the data plane.However, a forwarding configuration addressing the inherent resiliencychallenges to cope with unstable backhaul links using a combined RF LOS,NLOS and FSO has not been previously addressed. A resilient forwardingconfiguration of an SDN-based small cell wireless backhaul network 1806that focuses on SDN-based resiliency mechanisms and uses the concept ofOpenFlow fast failover groups 1808 as described hereinabove. Thecontroller 1802 calculates each link 1506 for each small cell node 1504backup links toward the Gateway. The main link and the backup link areboth placed into a fast failover group 1808. The small cell node 1504uses rapid link monitoring to locally detect if a link is in the outagestage, in which case, the OpenFlow-based fast failover locally switchesfrom a main link to a backup link.

The traditional SDN concept relies on a centralized control plane, whichexercises control on forwarding decisions in the data plane.Consequently, the control and data planes are decoupled which allows avery flexible forwarding control. However, using SDN for small cellbackhaul links present several challenges. This is because theperformance and reliability of mesh-based backhaul networks such as thatillustrated in FIG. 15 depends on fast local reactions to topologychanges where a centralized control plane is typically too slow toreact. Therefore, there been attempts to use proprietary routing andforwarding decisions based on distributed protocols were SDN is used tosteer traffic.

In an alternative approach as illustrated in FIG. 19, the forwardingdecisions inside the backhaul may be configured by the SDN controlplane. SDN-based resiliency using fast local restorations 1902 (e.g.implemented inside the data plane 1904 of the cell small backhaul nodes1906) may be used whenever local problems such as link outagetransitions of the millimeter wave backhaul links are detected. Thislocal repair mechanism, which can be preinstalled, avoids the need toask the controller how to react in a case when a neighbor node cannot bereached anymore and leads to a more robust data plane behavior.

Referring now to FIG. 20 there is illustrated the process forimplementing SDN-based local repair. The process uses SDN to calculate aprimary and a secondary path for small cell backhauling. SDN-based localrepair is implemented using fast failover groups 1808 (FIG. 18). Aprimary and a secondary action are put into the same group.Consequently, the SDN controller calculates for each small cell aprimary path at step 2002 towards the gateway. Additionally, the SDNcontroller calculates a backup path towards the gateway at step 2004.Based upon the path calculations, the SDN controller installs forwardingrules for the primary path at step 2006 into the fast failover group1808 and will additionally install forwarding rules at step 2008 for thebackup path into the fast failover group.

Once data packets arrive at a small cell node at step 1010 which shouldbe forwarded to a neighboring small cell node using mmWave links orother types of communications links, the data packets will be forwardedaccording to the first port in the fast failover group table whose portstate is active. This requires an OpenFlow data path implementationwhich uses for each neighbor a dedicated OpenFlow port. Once the primaryport is detected to be down, the data packets are automaticallyforwarded using the next active port, i.e. towards a different neighborwhere there is an active backup link. Thus, a determination is made atinquiry step 2002 if the primary path is working. If so, control passeson to step 2014, and the packet is forwarded on the port in the grouptable associated with the primary path. If inquiry step 2012 determinesthat the primary path is not working, the packet is forwarded on theport in the group table associated with the backup path at step 2016.The process is completed at step 2018. This process allows the smallcell node to perform a local failover instead of the SDN controllerperforming a centralized failover. This significantly reduces thereaction time to failures in the mesh forwarding structure.

Referring now to FIG. 21, there is illustrated the process for detectinglink state and transmitting on primary and backup links. In order todetect the link state, bidirectional forwarding detection (BFD) is acommonly used technology. BFD determines the state of the court byestablishing a connection at step 2102 using a three-way handshakeroutine. BFD next waits a predetermined period of time at step 2104 andthen transmits a periodic control message at step 2106. Inquiry step2108 determines if a response to the control message has been received.The timeout period is determined by the control messages between the BFDmessages. If a response to the control message is received,transmissions are carried out on the link at step 2110 and controlpasses back to step 2104 to await an additional predetermined period. Ifno response to the control message is received within a specified timeinterval, the link is considered down at step 2112. In this manner, linkfailures may be rapidly detected and reacted to. Consequently, smallcell backhaul nodes would send periodic BFD messages to each neighboringbackhaul node over the mmWave links to detect link states. Once BFDdetects a link down event at inquiry step 2108, the link state is set todown at step 2112. This triggers the OpenFlow datapath to starttransmitting to a different neighbor small cell. This is achieved byselecting a backup link at step 2114.

Alternatively, MAC layer protocol messages can be used in order to inferthe state of the mmWave backhaul links, which could be integrated intothe OpenFlow data path. The media access control (MAC) layer is a lowersublayer of the data link layer of the seven-layer OSI model. The OpenSystems Interconnection model (OSI model) is a conceptual model thatcharacterizes and standardizes the communication functions of atelecommunication or computing system without regard to their underlyinginternal structure and technology. Its goal is the interoperability ofdiverse communication systems with standard protocols. The modelpartitions a communication system into abstraction layers. The originalversion of the model defined seven layers.

A layer serves the layer above it and is served by the layer below it.For example, a layer that provides error-free communications across anetwork provides the path needed by applications above it, while itcalls the next lower layer to send and receive packets that comprise thecontents of that path. Two instances at the same layer are visualized asconnected by a horizontal connection in that layer.

The MAC sublayer provides adderessing in channel access controlmechanisms that make it possible for several terminals or network nodesto communicate with a multiple access network and incorporates a sharedmedium, e.g. an ethernet network. The hardware that implements the Macis referred to as the media access controller. The MAC sublayer axis thelogical link controller (LLC) sublayer and the networks physical layer.The MAC layer emulates a full-duplex logical communication channel in amultipoint network. The channel may provide unicast, multicast orbroadcast communication service.

A weakness with fast failover is that it can only perform localfailover. If no alternative local path is available, e.g. all neighborsare not reachable anymore, then crankback routing must be performed.This requires that the packet be sent backwards toward the source to asmall cell node which has an alternative active path towards thedestination. Thus, crankback forwarding can potentially have largeimpacts on the latency. Such latency can be reduced significantly byintroducing stateful forwarding in the data plane using OpenState.OpenState is a research effort focused in the development of a statefuldata plane API for Software-Defined Networking. OpenState is moreparticularly described in the OpenState v1.0 specification. If packetsarrive at a small cell forwarding node which does not have a next hoptowards the destination node because the link is down, the node tags thepacket and the packet is sent back towards the source. When the messagereaches the small cell node having a backup path, the state of theforwarding rules change in such a way that the coming packet traversethe backup path already at the node. Therefore, once a backup link isselected at step 2114, inquiry step 2116 determines if the backup linkis operating and available. If so, transmissions are then carried out onthe backup link at step 2118 and control passes back to step 2104. Ifthe backup link is not available as determined at inquiry step 2116, thecrankback forwarding process is carried out at step 2120 andtransmissions carried out on allocated available link.

It will be appreciated by those skilled in the art having the benefit ofthis disclosure that using LTE control channel to send openflow messagedirectly to small cells to reduce latency in an SDN-based multi-hopwireless backhaul network provides improved link reestablishment. Itshould be understood that the drawings and detailed description hereinare to be regarded in an illustrative rather than a restrictive manner,and are not intended to be limiting to the particular forms and examplesdisclosed. On the contrary, included are any further modifications,changes, rearrangements, substitutions, alternatives, design choices,and embodiments apparent to those of ordinary skill in the art, withoutdeparting from the spirit and scope hereof, as defined by the followingclaims. Thus, it is intended that the following claims be interpreted toembrace all such further modifications, changes, rearrangements,substitutions, alternatives, design choices, and embodiments.

What is claimed is:
 1. A system for providing small cell backhaulcommunication, comprising: a small cell backhaul network including aplurality of small cell network nodes; at least one mmWave transceiverat each of the plurality of small cell network nodes for establishingline-of-site (LOS) communication links with other small cell networknodes within the small cell backhaul network; at least one Non-Line ofSight (NLOS) sub-6 GHz transceiver at each of the plurality of smallcell network nodes for establishing the communications links with othersmall cell network nodes within the small cell backhaul network; atleast one Free Space Optics (FSO) transceiver at each of the pluralityof small cell network nodes for establishing the communications linkswith other small cell network nodes within the small cell backhaulnetwork; a software defined network (SDN) controller for controllingcommunication link configuration by the at least one mmWave transceiver,the at least one Non-Line of Sight (NLOS) sub-6 GHz transceiver and theat least one Free Space Optics (FSO) transceiver between the pluralityof small cell network nodes of the small cell backhaul network, whereinthe SDN controller further implements SDN based channel estimation tomultiplex between providing the communications link between the at leastone mmWave transceiver, the at least one NLOS sub-6 GHz transceiver andthe at least one FSO transceiver based upon communications linkconditions; and wherein the link configurations are established by theSDN controller using mmWave communications.
 2. The system of claim 1,wherein the SDN controller calculates for each of the communicationslinks within the small cell backhaul network a primary link and at leastone backup link.
 3. The system of claim 2, wherein the SDN controlleruses an SDN control plane to calculate the primary link and the at leastone backup link.
 4. The system of claim 2, wherein the SDN controllerstores forwarding rules based upon the calculated primary link and atleast one backup link in an OpenFlow Fast Failover Group.
 5. The systemof claim 1, wherein each of the plurality of small cell network nodes ofthe small cell backhaul network use rapid link monitoring to detect if aprimary communications link from a small cell network node has failed,if a failed primary communications link is detected the small cellnetwork node switches to a backup link stored in an OpenFlow FastFailover Group.
 6. The system of claim 1, wherein each of the pluralityof small cell network nodes of the small cell backhaul network usesBidirectional Forwarding Detection to determine if a communications linkhas failed.
 7. The system of claim 6, wherein each of the plurality ofsmall cell network nodes of the small cell backhaul network periodicallytransmits a Bidirectional Forwarding Detection message to eachneighboring small cell network node to detect communications linkstatus.
 8. The system of claim 6, wherein each of the plurality of smallcell network nodes of the small cell backhaul network periodicallytransmits a MAC layer protocol message to each neighboring small cellnetwork node to detect communications link status.
 9. The system ofclaim 6, wherein the plurality of small cell network nodes of the smallcell backhaul network uses crankback forwarding to establish a path to adestination when each of a primary link and a backup link for a smallcell network node is not working.
 10. A method for providing small cellbackhaul communication, comprising: establishing line-of-site (LOS)communication links from at least one of a plurality of small cellnetwork nodes within a small cell backhaul network with other small cellnetwork nodes within the small cell backhaul network using at least onemmWave transceiver; establishing the communication links with othersmall cell network nodes within the small cell backhaul network using atleast one Non-Line of Sight (NLOS) sub-6 GHz transceiver at each of theplurality of small cell network nodes; establishing the communicationlinks with other small cell network nodes within the small cell backhaulnetwork using at least one Free Space Optics (FSO) transceiver at eachof the plurality of small cell network nodes; controlling communicationlink configuration by the at least one mmWave transceiver, the at leastone Non-Line of Sight (NLOS) sub-6 GHz transceiver and the at least oneFree Space Optics (FSO) transceiver between the plurality of small cellnetwork nodes of the small cell backhaul network; and multiplexingbetween providing the communication link between the at least one mmWavetransceiver, the at least one NLOS sub-6 GHz transceiver and the atleast one FSO transceiver based upon communication link conditions. 11.The method of claim 10 further comprising calculating for each of thecommunications links within the small cell backhaul network a primarylink and at least one backup link with an SDN controller.
 12. The methodof claim 11, wherein the step of calculating further comprisescalculating the primary link and the at least one backup link using theSDN control plane of an SDN controller.
 13. The method of claim 11further comprising storing, by an SDN controller, forwarding rules basedupon the calculated primary link and at least one backup link in anOpenFlow Fast Failover Group.
 14. The method of claim 10 furthercomprising: detecting if a primary communications link from a small cellnetwork node has failed for each of the plurality of small cell networknodes of the small cell backhaul network using rapid link monitoring;and switching at the small cell network node to a backup link stored inan OpenFlow Fast Failover Group if a failed primary communications linkis detected.
 15. The method of claim 10 further comprising determiningat each of the plurality of small cell network nodes of the small cellbackhaul network if a communications link has failed using BidirectionalForwarding Detection.
 16. The method of claim 15 further comprisingperiodically transmitting from each of the plurality of small cellnetwork nodes of the small cell backhaul network a BidirectionalForwarding Detection message to each neighboring small cell network nodeto detect communications link status.
 17. The method of claim 15 furthercomprising periodically transmitting from each of the plurality of smallcell network nodes of the small cell backhaul network a MAC layerprotocol message to each neighboring small cell network node to detectcommunications link status.
 18. The method of claim 15 further comprisesestablishing a path to a destination when each of a primary link and abackup link for a small cell node is not working using crankbackforwarding at the plurality of small cells of the small cell backhaulnetwork.
 19. A system for providing small cell backhaul communication,comprising: a small cell backhaul network including a plurality of smallcell network nodes; at least one mmWave transceiver at each of theplurality of small cell network nodes for establishing communicationlinks with other small cell network nodes within the small cell backhaulnetwork; a software defined network (SDN) controller for controllingcommunication link configuration by the at least one mmWave transceiverbetween the plurality of small cell network nodes of the small cellbackhaul network, calculating for each of the communications linkswithin the small cell backhaul network a primary link and at least onebackup link and storing forwarding rules based upon the calculatedprimary link and at least one backup link in an OpenFlow Fast FailoverGroup; and wherein the link configurations are established by the SDNcontroller using mmWave communications.
 20. The system of claim 19further comprising: at least one Non-Line of Sight (NLOS) sub-6 GHztransceiver at each of the plurality of small cell network nodes forestablishing the communications links with other small cell networknodes within the small cell backhaul network; at least one Free SpaceOptics (FSO) transceiver at each of the plurality of small cell networknodes for establishing the communications links with other small cellnetwork nodes within the small cell backhaul network; and wherein theSDN controller further implements SDN based channel estimation tomultiplex between providing the communications links between the atleast one mmWave transceiver, the at least one NLOS sub-6 GHztransceiver and the at least one FSO transceiver based uponcommunication link conditions.
 21. The system of claim 19, wherein theSDN controller uses an SDN control plane to calculate the primary linkand the at least one backup link.
 22. The system of claim 19, whereineach of the plurality of small cells of the small cell backhaul networkuse rapid link monitoring to detect if a primary communications linkfrom a small cell backhaul node has failed, if a failed primarycommunications link is detected the small cell backhaul node switches toa backup link stored in an OpenFlow Fast Failover Group.
 23. The systemof claim 19, wherein each of the plurality of small cell network nodesof the small cell backhaul network uses Bidirectional ForwardingDetection to determine if a communications link has failed.
 24. Thesystem of claim 23, wherein each of the plurality of small cell networknodes of the small cell backhaul network periodically transmits aBidirectional Forwarding Detection message to each neighboring smallcell network node to detect communications link status.
 25. The systemof claim 23, wherein each of the plurality of small cell network nodesof the small cell backhaul network periodically transmits a MAC layerprotocol message to each neighboring small cell node to detectcommunications link status.
 26. The system of claim 23, wherein theplurality of small cell network nodes of the small cell backhaul networkuses crankback forwarding to establish a path to a destination when eachof primary link and backup link for a small cell network node is notworking.
 27. The system of claim 19, wherein the SDN controllerassociates at each small cell network node of the plurality of smallcell backhaul nodes a dedicated OpenFlow port for each neighboring smallcell network node.
 28. The system of claim 19, wherein the SDNcontroller associates a first OpenFlow port with the primarycommunications link and at least one second OpenFlow port with the atleast one backup link.